/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.ui.context.support;

import org.springframework.lang.Nullable;
import org.springframework.ui.context.HierarchicalThemeSource;
import org.springframework.ui.context.Theme;
import org.springframework.ui.context.ThemeSource;

/**
 * Empty ThemeSource that delegates all calls to the parent ThemeSource.
 * If no parent is available, it simply won't resolve any theme.
 *
 * <p>Used as placeholder by UiApplicationContextUtils, if a context doesn't
 * define its own ThemeSource. Not intended for direct use in applications.
 *
 * @author Juergen Hoeller
 * @see UiApplicationContextUtils
 * @since 1.2.4
 */
public class DelegatingThemeSource implements HierarchicalThemeSource {

    @Nullable
    private ThemeSource parentThemeSource;


    @Override
    public void setParentThemeSource(@Nullable ThemeSource parentThemeSource) {
        this.parentThemeSource = parentThemeSource;
    }

    @Override
    @Nullable
    public ThemeSource getParentThemeSource() {
        return this.parentThemeSource;
    }


    @Override
    @Nullable
    public Theme getTheme(String themeName) {
        if (this.parentThemeSource != null) {
            return this.parentThemeSource.getTheme(themeName);
        } else {
            return null;
        }
    }

}
